Environmental factors influence lesser scaup migration chronology and population monitoring

Abstract

Identifying environmental metrics specific to lesser scaup (Aythya affinis; scaup) spring migration chronology may help inform development of conservation, management and population monitoring. Our objective was to determine how environmental conditions influence spring migration of lesser scaup to assess the effectiveness of the Waterfowl Breeding Population and Habitat Survey in accurately estimating scaup populations. We first compared peak timing of mallard (Anas platyrhynchos) and scaup migration from weekly ground surveys in North Dakota, USA because the Waterfowl Breeding Population and Habitat Survey is designed to capture annual mallard migration. As predicted, we detected that peak timing of scaup and mallard migrations differed in 25 of 36 years investigated . We marked scaup with satellite transmitters (n ¼ 78; 7,403 locations) at Long Point, Lake Erie, Ontario, Canada; Pool 19 of the Mississippi River, Iowa and Illinois, USA; and Presque Isle Bay, Lake Erie, Pennsylvania, USA. We tested the assumption that our marked scaup were representative of the continental population using the traditional survey area by comparing timing of migration of marked birds and scaup counted in the North Dakota Game and Fish Department survey. We detected a strong positive correlation between marked scaup and the survey data, which indicated that marked scaup were representative of the population. We subsequently used our validated sample of marked scaup to investigate the effects of annual variation in temperature, precipitation, and ice cover on spring migration chronology in the traditional and eastern survey areas of the Waterfowl Breeding Population and Habitat Survey, 2005-2010. We evaluated competing environmental models to explain variation in timing and rate of scaup migration at large-scale and local levels. Spring migration of scaup occurred earlier and faster during springs with warmer temperatures and greater precipitation, variables known to influence energy budgets and wetland availability. Our results suggest that surveys designed to index abundance of breeding mallards is imprecise for estimating scaup abundance, and inaccurate at estimating breeding population size by survey stratum. Ó 2016 The Wildlife Society.

Evaluating the waterfowl breeding population and habitat survey for scaup

“…Use of the WBPHS data to infer spatial changes in breeding populations of scaup is clearly not appropriate (e.g., Afton and Anderson ; Ross et al ; Barker et al , ) because, as documented (this study, Finger et al ), they are still migrating to their breeding sites during the WBPHS. We detected that nearly half (48.8% of the total migrations) of our marked scaup using the traditional survey area were available to be counted more than once as they migrated north with the WBPHS crew.…”

“…One of our goals was to use environmental predictors of date of settling outlined in Finger et al () and determine metrics from this study that could be used in the future to refine WBPHS scaup population estimates. Austin et al (), Mallory et al (), and Finger et al () suggested using weather data to adjust the population estimates of the WBPHS, but we caution against such an approach given the clear biases we detected. Development of models that include metrics such as survey stratum latitude and annual spring environmental conditions might potentially be used to improve scaup breeding population estimates derived from the WBPHS, but independent annual population estimates derived from banding data would be necessary to evaluate such models (Arnold et al , ; Koons et al ).…”

“…Maintaining consistency in survey methodology is important (Cowardin and Blohm ), but a periodic review of methods and evaluations of bias are needed. Improvements to surveys and population models also may be required as science‐based information on environmental factors influencing waterfowl migration chronology, and timing and locales of settling on breeding sites become available (Cowardin and Blohm , Austin et al , Mallory et al , Finger et al ). Evaluations of the WBPHS have become increasingly important because responses (e.g., migration chronology and timing of settling) to climate change are likely to vary among species (Gurney et al , Drever et al , Notaro et al , Osnas et al , Zhao et al ).…”

Understanding the demographic drivers of realized population growth rates

“…, Finger et al. ). Integrated analyses can be used to reconcile such problems with more accurate data that are collected at fewer locations (Hanks et al.…”

“…The WBPHS is not well timed for accurately estimating Lesser Scaup abundance because the birds are still migrating (i.e., moving among strata) during the survey period and also settle in non‐surveyed areas (Finger et al. ).…”